There has been proposed an image forming apparatus such as a laser printer that includes a developing device for circulating developer between a toner cartridge for accommodating the developer and a frame to which the toner cartridge is detachably attached.
For example, JP-A-9-319202 discloses a developing device including a toner cartridge and a frame, in which a toner supply port for mutually communicating the inside of the frame to the inside of the toner cartridge is formed in a position corresponding to substantially center of the toner cartridge, and a pair of toner suction ports are formed in both sides of the toner supply port.
The developing device includes a developing roller, and an auger roller for rotating around a shaft extending along a longitudinal direction of the developing roller.
In this developing device, toner inside of the toner cartridge is supplied to the auger roller through the toner supply port, and the toner is supplied to the side of the developing roller while the toner being transported toward both ends in a direction (i.e., longitudinal direction of the developing roller) of the shaft by the auger roller. Then, the toner which has not been supplied to the side of the developing roller is circulated between the toner cartridge and the frame by being returned from each of the toner suction ports to the toner cartridge.
In this developing device disclosed in JP-A-9-319202, each of the toner suction ports is arranged between both ends of the shaft direction of the auger roller. Thus, the toner supplied from the toner supply port to the auger roller may be returned from each of the toner suction ports to the toner cartridge in the process of being transported to both ends of the shaft direction of the auger roller. In this case, the toner is not transported to both ends of the shaft direction of the auger roller. Thus, the toner may not be sufficiently supplied to both ends of the longitudinal direction of the developing roller.